1. Field of the Invention
The present invention relates to methods and apparatus for organizing selection of operational parameters in communication systems and, more particularly, to techniques for coordinating selection of parameters used to communicate between network nodes on a message-by-message basis by performing vector transformations of parameters organized into system state vectors, as a function of observed communication channel characteristics, operational requirements, and pre-computed performance data.
2. Description of the Related Art
The purpose of any communication system is to effectively transmit and receive information over a particular channel or communication medium. As mobile communication devices are increasingly used and the need for reliable and continuous communications systems becomes greater, government, military and industry leaders alike are working to solve sophisticated problems in a reliable and cost-effective manner. For instance, certain communications problems are often encountered in commercial and military applications where the communications network is required to maintain a reliable and continuous (uninterrupted) high data rate radio frequency (RF) communications in harsh environments, while network members (nodes) are consistently on the move. Furthermore, it is often desirable to establish and maintain communications without the aid of a base station or any other reference signal over the air. For example, in modem battlefield communications where troops are constantly on the move, the communication system is often subjected to intentional jamming or unintentional interference. In addition, potentially severe multipath interference conditions may limit or severely cripple strategic communication lines. Such communication systems are often ineffective if they rely on synchronization signals, as such signals may be detected and exploited by an adversary. Moreover, military operations occur in a variety of environments including indoors, outdoors, urban, suburban and exurban environments where propagation signal characteristics vary greatly. Similarly, commercial systems working in overcrowded frequency bands also encounter interference difficulties which prevent maintaining reliable communications.
Communications systems such as Cellular Communications, personal communications systems (PCS) and wireless local area networks (LANs) are examples of systems and applications designed to solve such mobile communications problems. However, certain significant drawbacks associated with each of the above communications systems exist. First, cellular communications rely on fixed base stations to establish and maintain communications among the mobile units. In this environment, all communications are routed to and from the base station. In addition, base stations aid in performing multipath countermeasures implemented in those systems. The same concept is applied in personal communications systems.
Wireless LANs can operate in a peer-to-peer manner in a limited area, but require a time synchronization signal emitted by the access points for extended service. Additional shortcomings of these systems include the fact that the use of base stations, whether fixed or mobile, constitutes a single point of failure, and base stations are not compatible with highly mobile networks. Furthermore, a base station presents a conspicuous target, from the electromagnetic emissions point of view, thus making it unsuitable for a hostile environment like battlefield applications, since a base station can be easily detected and targeted with homing weapons. In civilian applications, regulations allocating frequency bands and physical spacing between transmitters minimize the requirements for countermeasures. This is not the case with battlefield applications, where the system has to work reliably, particularly in the presence of intentional (hostile) interference.
Wireless LANs which operate in Time Division Multiple Access (TDMA) systems, e.g. Digital European Cordless Telephone (DECT), also have the base station problem mentioned above. LANs which rely on carrier sense multiple access with collision avoidance (CSMA/CA), given the small Processing Gain (PG) of less than 11 dB, can operate in a limited peer-to-peer mode; however, such LANs have no means to combat call collisions even with a relatively small number of users (e.g., five or six). None of these systems has any means to account for network members coming in and out of direct line of sight range. Wireless LANs working in CSMA/CA mode rely on access points to handle increased numbers of users. An access point fulfills the same role as a base station.
Given the number and complexity of parameters which have to be varied and/or adapted to the environment, any attempt to control classical communications parameters without a systematic way of combining and selecting which parameters to change, dooms any system to poor performance and to be plagued by reliability problems. This is, indeed, very noticeable in current Cellular and Personal Communications System, where communications cannot be maintained in a reliable fashion.